Molding method and molding apparatus

ABSTRACT

The present invention relates to a molding method of reducing a diameter in an end portion of a metal tube to be characterized in having a step of rotating a metal tube around an axial core or rotating a frame in which a plurality of ring-shaped tools are arranged, and moving the axial core of the ring-shaped tool away from the axial core of the metal tube while moving the metal tube or the frame, thereby reducing the diameter in an end portion of the metal tube.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus for reducing a diameter in an end portion of a metal tube, and more particularly to a molding method of reducing a diameter in a tapered shape while holding an axial core coinciding with an axial core of a metal tube, or reducing a diameter in the tapered shape while holding the axial core which is eccentric with respect to the axial core of the metal tube, and further reducing a diameter in the tapered shape by inclining the axial core of the reduced diameter portion with respect to the axial core of the metal tube, and a molding apparatus which can achieve the molding method.

2. Description of the Related Art

It has been executed to reduce a diameter in an end portion of a cylindrical metal tube so as to mold in a tapered shape by employing a rotational molding method. As the rotational molding method, there are a spinning molding method, an eccentric rotational molding method and the like, as described in Pipe Working Method, Second Edition (Publishing Office: Nikkan Kogyo Shinbun: Sep. 30, 1998).

The spinning molding method is structured such as to reduce a diameter in an end portion of a metal tube by employing a roller which is brought into contact with an outer peripheral surface of the metal tube to be reduced in the diameter, bringing the roller into pressure contact with the outer peripheral surface of the metal tube, and moving the roller close to an axial core of the metal tube as well as relatively moving the metal tube and the roller along the axial core of the metal tube while rotating the metal tube or rotating the roller around the axial core of the metal tube serving as a center of rotation.

In this spinning molding method, it is necessary to make a molding load in an axial direction small in order to prevent a buckling of the metal tube from being generated. Accordingly, it is preferable to be employed at a time of reducing a diameter in a thin metal tube, however, since a working rate at one time is small, it is necessary to repeat a working step of moving the roller from a start point of the diameter reduction to an end point at several times, so that there is a problem that a limit is generated in shortening of a working time.

The eccentric rotational molding method is structured such as to reduce a diameter in an end portion of a metal tube by employing a rotatable conical tool, arranging an axial core of the conical tool in parallel to an axial core of the metal tube so as to bring a conical surface of the conical tool into pressure contact with the end portion of the metal tube, and moving the conical tool in a direction in which the axial core of the conical tool moves close to the axial core of the metal tube along the axial core or in a direction in which the axial core of the conical tool moves away from the axial core of the metal tube in parallel, while rotating the metal tube.

In this eccentric rotational molding method, there is obtained an advantage that it is possible to enlarge a molding load with respect to the axial direction, it is possible to basically mold by one work, and a molding speed becomes high.

As an apparatus for molding the diameter reduction in the tube while bringing out the advantage mentioned above, there has been proposed a technique described in Japanese Patent No. 2548799. In this technique, the tube is molded so as to reduce the diameter from the end portion by making a center of rotation of a metal mold having a conical hole and being rotatable eccentric from a center axis of the tube, moving the end portion of the tube in a direction of the metal mold along the center axis while bringing the end portion of the tube into pressure contact with the conical hole and rotating the tube. In the technique of Japanese Patent No. 2548799, it is possible to mold so as to reduce the diameter not only in the end portion of the tube but also over an optional length.

SUMMARY OF THE INVENTION

As mentioned above, in the case of employing the spinning molding method at a time of reducing the diameter in the end portion of the metal tube, there is a problem that the molding speed becomes slow, and the limit is generated in the shortening of the working time.

Further, the technique described in Japanese Patent No. 2548799 is advantageously employed at a time of molding so as to reduce the diameter in the end portion of the tube, however, there is always a requirement of developing a more rational molding method. Particularly, in the technique in Japanese Patent No. 2548799, there is a risk of generating a problem that a molding load applied to the tube becomes large by enlarging an offset amount between the center of rotation of the metal mold and the center axis of the tube, and the buckling is generated. Accordingly, there is demanded to develop a technique in which a molding speed is fast so as to intend to shorten a working time without generating a buckling.

In order to solve the problem mentioned above, in accordance with a first aspect of the present invention, there is provided a molding method of reducing a diameter in an end portion of a metal tube including the steps of arranging a plurality of ring-shaped tools arranged with an axial core which is in parallel to an axial core of the metal tube having the end portion to be reduced in the diameter and having an inner periphery brought into contact with an outer periphery of the metal tube, in a radial direction of a frame having an axial core which is in parallel to the axial core of the metal tube, arranging the plurality of ring-shaped tools in such a manner that an axial core of each of the ring-shaped tools is in parallel to the axial core of the metal tube and an inner periphery is brought into contact with the outer periphery of the metal tube or is not brought into contact therewith, and arranging so as to pinch the metal tube, and thereafter rotating the metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged, and moving the axial core of the ring-shaped tool away from the axial core of the metal tube while moving the metal tube or the frame, thereby reducing the diameter in the end portion of the metal tube.

In the molding method mentioned above, it is preferable to reduce the diameter in the end portion of the metal tube in a tapered shape having an axial core coinciding with the axial core of the metal tube, by previously bringing the axial core of the metal tube into line with the axial core of the frame. Further, in the case of reducing the diameter in the tapered shape having the axial core which is eccentric from the axial core of the metal tube, it is preferable to previously make the axial core of the metal tube eccentric from the axial core of the frame. Further, in the case of reducing the diameter in the end portion of the metal tube in the tapered shape having the axial core which is eccentric with respect to the axial core of the metal tube, it is preferable to rotate the metal tube around the axial core or rotate the frame in which a plurality of ring-shaped tools are arranged, move the metal tube or the frame in a direction in which the ring-shaped tools reach the end portion of the metal tube, and moving the axial core of the ring-shaped tools away from the axial core of the metal tube while moving the axial core of the metal tube away from the axial core of the frame in parallel.

Further, in accordance with a second aspect of the present invention, there is provided a molding method of reducing a diameter in an end portion of a metal tube while inclining at least a partial axial core of the end portion to be reduced in the diameter with respect to an axial core of the metal tube, at a time of reducing the diameter in the end portion of the metal tube, including the steps of: arranging a plurality of ring-shaped tools rotating in a state in which an inner periphery is brought into contact with an outer periphery of the metal tube, in a radial direction of a frame and structuring an axial core of the frame and the axial core of the metal tube in such a manner as to be relatively changeable, setting the axial core of the frame to a previously set angle with respect to the axial core of the metal tube and arranging the plurality of ring-shaped tools in such a manner that the inner periphery of each of the ring-shaped tools is brought into contact with the outer periphery of the metal tube or is not brought into contact therewith, arranging so as to pinch the metal tube in the plurality of ring-shaped tools, thereafter rotating the metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged, and moving the metal tube or the frame, and moving the axial core of the ring-shaped tool away from the axial core of the metal tube while relatively changing the axial core of the frame and the axial core of the metal tube or without changing, in the process of moving the metal tube or the frame, thereby reducing the diameter in the end portion of the metal tube.

In the molding method mentioned above, it is preferable to reduce the diameter in the end portion of the metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube, by previously bringing the axial core of the metal tube into line with the axial core of the frame, and relatively moving the axial core of the frame and the axial core of the metal tube in parallel in the process of moving the metal tube or the frame as well as rotating the metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.

Further, in the molding method mentioned above, it is preferable to reduce the diameter in the end portion of the metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube by previously inclining the axial core of the metal tube and the axial core of the frame relatively, and maintaining the incline between the axial core of the metal tube and the axial core of the frame in the process of moving the metal tube or the frame as well as rotating the metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.

Further, in the molding method mentioned above, it is preferable to reduce the diameter in the end portion of the metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube, by setting the axial core of the metal tube and the axial core of the frame to a previously set angle, and relatively changing the angle between the axial core of the metal tube and the axial core of the frame together with the movement of the metal tube or the frame, in the process of moving the metal tube or the frame as well as rotating the metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.

Further, in accordance with the present invention, there is provided a molding apparatus for reducing a diameter in an end portion of a metal tube, including a plurality of ring-shaped tools rotating in a state in which an inner periphery is brought into contact with an outer periphery of the metal tube, a frame arranging and holding the plurality of ring-shaped tools in a radial direction, a tool moving member provided in the frame and moving the individual ring-shaped tool within a surface which is orthogonal to an axial core of each of the ring-shaped tools, a drive member rotating the frame, a grip member arranged so as to face to the frame and gripping the metal tube to be reduced in diameter in the end portion, and a supply car mounting the grip member and structured such as to be movable in a direction of moving the grip member close to or away from the frame, and an orthogonal direction to the direction.

In the molding apparatus mentioned above, it is preferable to have a revolving member provided in the frame or the grip member arranged so as to face to the frame and relatively changing the angle formed by the axial cores.

Further, in the molding apparatus mentioned above, it is preferable that a plurality of ring-shaped tools held by the frame are arranged at a uniform angle around the axial core of the frame, and it is further preferable that they are arranged at positions facing at 180 degree.

In accordance with the molding method on the basis of the first aspect of the present invention, since the structure is made such as to arrange a plurality of ring-shaped tools in the outer periphery of the metal tube to be reduced in diameter and make the axial core of the ring-shaped tool eccentric with respect to the axial core of the metal tube, it is possible to execute a rational eccentric rotational molding with respect to the metal tube by the individual ring-shaped tools. In other words, since the eccentric rotational molding method can enlarge the molding load in comparison with the spinning molding method, the eccentric rotational molding method has a feature capable of making the molding speed faster. In particular, it is possible to enlarge a total of the molding loads applied to the metal tube by bringing a plurality of ring-shaped tools into contact with the metal tube so as to simultaneously mold. Accordingly, it is possible to improve a diameter reducing rate. Therefore, it is possible to intend to shorten a working time. Further, it is possible to lighten the load applied to the individual ring-shaped tool, and it is possible to secure a high molding precision.

Further, it is possible to reduce the diameter in the end portion of the metal tube in the tapered shape having the axial core coinciding with the axial core of the metal tube, by attaching a plurality of ring-shaped tools to the frame, bringing the axial core of the metal tube into line with the axial core of the frame, and molding while keeping this state. Further, it is possible to reduce the diameter in the tapered shape having the axial core which is eccentric from the axial core of the metal tube, by making the axial core of the metal tube eccentric from the axial core of the frame, and molding while keeping this state. Further, it is possible to reduce the diameter in the end portion of the metal tube in the tapered shape having the axial core which is eccentric from the axial core of the metal tube, by moving the axial core of the ring-shaped tools from the axial core of the metal tube while moving the axial core of the metal tube away from the axial core of the frame in parallel.

Further, in accordance with the molding method on the basis of the second aspect of the present invention, since the structure is made such as to arrange a plurality of ring-shaped tools in the outer periphery of the metal tube to be reduced in diameter and make the axial core of the ring-shaped tool eccentric with respect to the axial core of the metal tube, it is possible to execute a rational eccentric rotational molding with respect to the metal tube by the individual ring-shaped tools. In other words, since the eccentric rotational molding method can enlarge the molding load in comparison with the spinning molding method, the eccentric rotational molding method has a feature capable of making the molding speed faster. In particular, it is possible to enlarge a total of the molding loads applied to the metal tube by bringing a plurality of ring-shaped tools into contact with the metal tube so as to simultaneously mold. Accordingly, it is possible to improve a diameter reducing rate. Therefore, it is possible to intend to shorten a working time. Further, it is possible to lighten the load applied to the individual ring-shaped tool, and it is possible to secure a high molding precision.

Further, since the structure is made such as to attach a plurality of ring-shaped tools to the frame and make the axial core of the frame and the axial core of the metal tube relatively changeable, it is possible to set the axial core of the frame to a desired angle with respect to the axial core of the metal tube. Accordingly, it is possible to reduce the diameter in the end portion of the metal tube in the tapered shape having the axial core inclined at the desired angel with respect to the axial core of the metal tube, by setting the axial core of the frame to the previously set angle with respect to the axial core of the metal tube, and molding in this state.

Further, it is possible to reduce the diameter in the end portion of the metal tube in the tapered shape having the axial core inclined with respect to the axial core of the metal tube, by relatively inclining the axial core of the metal tube and the axial core of the frame, and maintaining the incline between the axial core of the metal tube and the axial core of the frame in the process of moving the metal tube or the frame while rotating the metal tube or the frame.

In other words, it is possible to form the reduced diameter portion which is inclined with respect to the axial core of the metal tube in the end portion of the metal tube, by changing a relation between the axial core of the metal tube and the axial core of the frame to which a plurality of ring-shaped tools are attached.

In the molding method in accordance with the present invention, it is preferable that at least a part of the axial core of the reduced diameter portion obtained by reducing the diameter in the end portion of the metal tube is inclined with respect to the axial core of the metal tube. For example, it is possible to reduce the diameter in such a manner as to bring the axial core at a predetermined length in the metal tube side in the reduced diameter portion into line with the axial core of the metal tube, and incline the axial core of a continuous position with the predetermined length portion with respect to the axial core of the metal tube. Further, it is possible to make the axial core in the predetermined length portion of the end portion in an open side in the reduced diameter portion in parallel to the axial core of the metal tube.

Further, the molding apparatus in accordance with the present invention can preferably execute the molding method mentioned above, and can reduce the diameter in the end portion of the metal tube in the desired shape.

Further, in the molding apparatus mentioned above, in the case of arranging a plurality of ring-shaped tools held to the frame at the uniform angle around the axial core of the frame, particularly, at the positions facing at 180 degree, it is possible to prevent the buckling of the metal tube in accordance with the molding, and it is possible to achieve the diameter reducing work having a high molding precision.

Further, the molding method or the molding apparatus in accordance with the present invention is advantageously executed at a time of working an exhaust gas converter of a motor vehicle, and particularly includes a terminal diameter reducing work of a position to which the flange is attached for connecting the exhaust gas converter and an exhaust gas silencer, at a time of working the exhaust gas converter. There has been known that a dimensional precision of a diameter in the work mentioned above, largely affects a weld quality of the weld bonded flange, however, since the present invention can quickly and precisely work the weld portion as mentioned above, there can be obtained an effect that it is possible to reduce a generation of a poor weld in the weld bonded portion without extending a time required for the diameter reducing work.

Further, the molding method or the molding apparatus in accordance with the present invention is advantageous at a time of working the exhaust gas converter of the motor vehicle. In other words, it is possible to smoothly and precisely execute the work of reducing the diameter in the end portion of the metal tube, by arranging an assembly obtained by winding a mat around a ceramic catalyst carrier in an inner portion of the metal tube, prior to working the end portion of the metal tube so as to reduce the diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view schematically explaining a structure of a molding apparatus.

FIG. 2 is a plan view schematically explaining the structure of the molding apparatus.

FIG. 3 is a view explaining a structure of a ring-shaped tool.

FIGS. 4A and 4B are views explaining a principle of a molding method in accordance with the present invention.

FIGS. 5A and 5B are views explaining a shape of a reduced diameter portion in which a diameter is reduced in accordance with a first molding method of the present invention.

FIGS. 6A to 6C are views explaining a shape of a reduced diameter portion in which a diameter is reduced in accordance with a second molding method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A description will be given below of a preferable embodiment of a molding apparatus in accordance with the present invention with reference to the accompanying drawings, and also given of a molding method. FIG. 1 is a side elevational view schematically explaining a structure of a molding apparatus. FIG. 2 is a plan view schematically explaining the structure of the molding apparatus. FIG. 3 is a view explaining a structure of a ring-shaped tool. FIGS. 4A and 4B are views explaining a principle of a molding method in accordance with the present invention. FIGS. 5A and 5B are views explaining a shape of a reduced diameter portion in the case that an axial core of a metal tube and an axial core of the reduced diameter portion are inclined. FIGS. 6A to 6C are reference views explaining a procedure of reducing a diameter in an end portion of the metal tube.

Embodiment 1

First, a description will be given of the principle of the molding method in accordance with the present invention with reference to FIGS. 4A and 4B. The molding method in accordance with the present invention is structured such as to arrange a plurality of ring-shaped tools rotatably structured in such a manner as to be brought into contact with the metal tube while pinching an outer periphery of the metal tube to be reduced in diameter, and press the outer periphery of the metal tube by an inner periphery of the individual ring-shaped tool by moving the metal tube and the ring-shaped tools along an axial core (which is inclined at a previously set angle with respect to the axial core of the metal tube) of the reduced diameter portion as well as moving the axial core of the ring-shaped tool away from the axial core of the metal tube, while relatively rotating the metal tube and the ring-shaped tools, thereby reducing the diameter of the metal tube.

For example, an inner periphery of a ring-shaped tool 2 structured rotatable (rotatable on its own axis) around an axial core 2 a serving as a center is brought into contact with an outer periphery of a metal tube to be reduced in diameter. At this time, it is assumed that a distance between the axial core 2 a of the ring-shaped tool 2 and an axial core 1 a of the metal tube is OF-A shown in FIG. 4A. If the ring-shaped tool 2 is rotated around the axial core 1 a of the metal tube under this state, a circle 3 having a diameter ΦD is formed by a circular arc of the ring-shaped tool 2, as shown in the same drawing, however, the circle 3 is identical to an outer diameter of the metal tube 1, and the diameter reduction of the metal tube is not executed in this state.

Next, as shown in FIG. 4B, the distance of the axial core 2 a of the ring-shaped tool 2 from the axial core 1 a of the metal tube is changed to OF-B which is larger than OF-A, and if the ring-shaped tool 2 is rotated around the axial core 1 a in this state, a circle 4 having a smaller diameter Φd than the diameter (D is formed by the circular arc of the ring-shaped tool 2, as shown in the same drawing. At this time, a changing amount of the ring-shaped tool 2 comes to a molding load applied to the metal tube, and an outer diameter of the metal tube is reduced in diameter from ΦD to Φd.

As mentioned above, it is possible to reduce the diameter in the end portion of the metal tube, by continuously changing a displacement amount of the axial core 2 a of the ring-shaped tool 2 from the axial core 1 a of the metal tube, and continuously changing the metal tube or the ring-shaped tool 2 along the axial core 1 a.

Accordingly, it is possible to form two circles around the axial core 1 a, for example, by arranging a plurality of (for example, two) ring-shaped tools 2 along the axial core 1 a of the metal tube so as to be close to each other, and rotating the ring-shaped tools 2 around the axial core 1 a of the metal tube in a state in which the distances of the axial cores 2 a of the respective ring-shaped tools 2 from the axial core 1 a are different. In this case, it is possible to execute the diameter reduction with respect to the metal tube by pressing inner peripheries of two ring-shaped tools 2 to the outer periphery of the metal tube by moving the ring-shaped tools 2 in a direction in which the axial core 2 a moves away from the axial core 1 a of the metal tube, while rotating the metal tube on its own axis or rotating two ring-shaped tools 2 around the axial core 1 a.

Further, it is possible to form approximately one circle around the axial core 1 a by forming contact positions of two ring-shaped tools 2 with respect to the metal tube in a protruded shape, arranging the protruded portions so as to be close to each other, and rotating the ring-shaped tools around the axial core 1 a of the metal tube in a state in which distance of the axial cores 2 a of the respective ring-shaped tools 2 from the axial core 1 a become equal. In this case, it is possible to execute the diameter reduction with respect to the metal tube, by pressing the extremely close positions in the direction of the axial core 1 a in the outer periphery of the metal tube by two ring-shaped tools 2 so as to pinch, by moving two ring-shaped tools 2 in a direction in which the axial cores 2 a simultaneously move away from the axial core 1 a of the metal tube. Accordingly, it is possible to apply a greater molding load to the individual ring-shaped tool 2 while preventing a buckling which may be generated in the metal tube, and it is possible to improve a molding efficiency.

As mentioned above, in accordance with the present invention, the diameter reduction molding is simultaneously executed with respect to the metal tube by two ring-shaped tools 2. Accordingly, it is possible to set a magnitude of the molding load applied to the individual ring-shaped tool 2 to a suitable value, it is possible to achieve a secure molding by one step. In other words, it is possible to improve a working rate by applying the same molding load to each of the ring-shaped tools 2, and it is possible to set the molding load in such a manner that a coarse molding is executed by the preceding ring-shaped tool 2 and a finish molding is executed by the subsequent ring-shaped tool 2.

In this case, in the same drawing, the diameter ΦD of the circle 3 comes to twice as much as a value obtained by subtracting the distance OF-A between the axial core 1 a and the axial core 2 a from a radius of the ring-shaped tool 2. In the same manner, the diameter Φd of the circle 4 comes to twice as much as a value obtained by subtracting the distance OF-B between the axial core 1 a and the axial core 2 a from the radius of the ring-shaped tool 2. Accordingly, it is possible to reduce a diameter of a circle formed by the circular arc of the ring-shaped tool 2 (reduce a diameter in the end portion of the metal tube), by changing an interval (enlarging the interval) between the axial core 2 a of the ring-shaped tool 2 and the axial core 1 a of the metal tube.

A speed which moves the axial core 2 a of the ring-shaped tool 2 away from the axial core 1 a of the metal tube can be appropriately set in correspondence to a condition such as a material, a thickness or the like of the metal tube, and can not be definitely set.

The number of the ring-shaped tool is not particularly limited, but it is preferable that at least two ring-shaped tools are provided. In particular, the pressing positions of the ring-shaped tools 2 to the metal tube face to each other by arranging two ring-shaped tools 2 on a diameter centering on the axial core 1 a of the metal tube (at positions facing at 180 degree). Accordingly, it is possible to prevent the buckling which may be generated in the metal tube so as to apply a greater molding load. This case is advantageously employed at a time of molding with respect to the metal tube in which the thickness is thin and the risk that the buckling is generated is high.

Particularly, in the case that three or more ring-shaped tools are arranged, it is preferable to set the moving directions of the respective ring-shaped tools to an equal angle within a surface orthogonal to the axial core 1 a of the metal tube, and set such that the applying methods of the molding loads are balanced at a time of executing the molding work with respect to the metal tube. In this case, the total of the molding loads applied to the metal tube becomes large at a degree that the number of the ring-shaped tool is increased. Accordingly, this structure is advantageously employed in a case of molding a thick metal tube.

In the present invention, since the inner periphery of the ring-shaped tool is brought into contact with the outer periphery of the metal tube to be reduced in diameter, it is necessary that the inner diameter is larger than the outer diameter of the metal tube. Further, since it is necessary that the ring-shaped tool is brought into contact with the outer periphery of the metal tube so as to rotate on its own axis, it is preferable to form a whole of the ring-shaped tool as a rolling bearing structure.

It is not limited whether the metal tube is rotated or a plurality of ring-shaped tools 2 are rotated, at a time of molding the metal tube. Whichever may be rotated, no special problem is generated. Particularly, in the case that a plurality of ring-shaped tools are rotated, there is generated a risk that a dynamic balance is not secured, however, in this case, since the rotating speed at a time of rotating is not large, there is not generated any problem.

Embodiment 2

Next, a description will be given of a structure of a molding apparatus A in accordance with the present embodiment with reference to the accompanying drawings. The molding apparatus A shown in the drawing is structured such that a diameter reduction can be executed at an axial core inclined with respect to the axial core 1 a of the metal tube 1 in the end portion of the metal tube 1, by gripping the metal tube 1 to be reduced in diameter in the end portion, arranging two ring-shaped tools 11 and 12 in the outer periphery of the end portion of the metal tube 1, and moving the ring-shaped tools 11 and 12 in a direction crossing to the axial core 1 a as well as moving the metal tube 1 in a direction moving the metal tube 1 away from or close to the ring-shaped tools 11 and 12, while rotating the ring-shaped tools 11 and 12.

The molding apparatus A has a supply car 22 mounted to a pair of rails 21, and the supply car 22 is structured such as to be driven by a supply car driving apparatus 23 constituted by a servo motor 23 a and a ball spline 23 b so as to be movable in directions of arrows a and b along an installing direction of the rail 21. Accordingly, it is possible to move the supply car 22 at a desired speed in the direction of the arrow a or the direction of the arrow b along the rail 21, by driving the servo motor 23 a.

A carriage 26 mounting a chuck 25 forming a grip member detachably gripping the metal tube 1 is arranged in the supply car 22, and the carriage 26 is driven by a carriage driving apparatus 27 constituted by a servo motor 27 a and a ball spline 27 b so as to be movable in directions of arrows c and d corresponding to a direction orthogonal to the installing direction of the rail 21 and a direction moving close to or away from the ring-shaped tools 11 and 12 (a frame 31 mentioned below). Accordingly, it is possible to move the carriage 26 at a desired speed in the direction of the arrow c or the direction of the arrow d corresponding to the orthogonal direction to the rail 21, by driving the servo motor 27 a.

The chuck 25 detachably gripping the metal tube 1 is mounted via a rotating table 28 serving as a revolving member provided in the carriage 26 constructing the supply car 22. The structure of the rotating table 28 is not particularly limited, but may be formed as a general structure which has a driving means (not shown) and is used as a rotating tool. The chuck 25 is fixed to a center of rotation of the rotating table 28, and is structured such as to freely revolve in directions of arrows e and f in accordance with the rotation of the rotating table 28. Accordingly, it is possible to revolve the chuck 25 at a desired speed in the direction of the arrow e or the direction of the arrow f around the center of rotation by driving the driving means (not shown).

In the supply car 22 structured as mentioned above, it is possible to set a revolving angle of the chuck 25 to a desired angle and set a position within a plane of the chuck 25 to a desired position, as shown in FIG. 2, by synchronizing operations of the supply car driving apparatus 23, the carriage driving apparatus 27 and the rotating table 28.

Two ring-shaped tools 11 and 12 are arranged so as to face at 180 degree on a straight line 31 b passing through a center 31 a of a ring-shaped frame 31, as shown in FIG. 3, and are attached to a rod 32 a of a hydraulic cylinder 32 forming a tool moving member attached to the frame 31. A pair of guide bars 33 are provided in an inner peripheral surface of the frame 31 in parallel to the straight line 31 b of the frame 31 in correspondence to the respective ring-shaped tools 11 and 12. Further, the structure is made such that each of the ring-shaped tools 11 and 12 is guided by the corresponding guide bar 33, whereby each of the axial cores 11 a and 12 a can accurately move on the straight line 31 b with respect to the center 31 a of the frame 31 (the axial core of the frame 31). Further, the guide bar 33 has a function of countering a thrust load applied to each of the ring-shaped tools 11 and 12 at a time of molding with respect to the metal tube 1, in addition to a function of guiding the moving direction of each of the ring-shaped tools 11 and 12.

The ring-shaped tools 11 and 12 have a function of transmitting the molding load applied from the hydraulic cylinder 32 as well as being brought into contact with the outer periphery of the metal tube 1, and have molding rings 11 b and 12 b structured such as to rotate on its own axis on the basis of a contact friction with the metal tube 1. The inner surfaces of the molding rings 11 b and 12 b may be formed in a tapered shape, however, in this case, there is a risk that a general-purpose property of a working condition including a taper angle formed in the metal tube 1 is deteriorated.

Accordingly, the present embodiment is structured such that the molding can be executed by forming rims 11 c and 12 c in which end portions in one side are protruded, and bringing the rims 11 c and 12 c into pressure contact with the outer periphery of the metal tube 1. In particular, in the present embodiment, the rims 11 c and 12 c formed in the molding rings 11 b and 12 b of the ring-shaped tools 11 and 12 are arranged in such a manner as to be capable of being adjacent to each other, and the structure is made such as to be capable of simultaneously molding extremely close positions of the metal tube 1 by the respective rims 11 c and 12 c. Since the ring-shaped tools 11 and 12 are structured as mentioned above, it is possible to apply the molding load to the metal tube 1 approximately on the straight line 31 b, and it is possible to prevent the bucking from being generated.

Each of the molding rings 11 b and 12 b is rotatably supported to the bearing member 13 attached to the rod 32 a of the hydraulic cylinder 32, thereby being structured such as to freely rotate on its own axis. In other words, a ring-shaped case 13 a is attached to the rod 32 a of the hydraulic cylinder 32, a bearing 13 b is arranged in the case 13 a, and the molding bearings 11 b and 12 b are pressure inserted to an inner ring of the bearing 13 b. A fitting portion 13 c fitted to the guide bar 33 is formed at a predetermined position on an outer periphery of the case 13, and the fitting portion 13 c is fitted to the guide bar 33, whereby it is possible to move each of the ring-shaped tools 11 and 12 along the straight line 31 b in accordance with the drive of the hydraulic cylinder 32.

Further, flanges 11 d and 12 d are respectively provided in the molding rings 11 b and 12 b, and the structure is made such as to transmit the thrust load applied to the molding rings 11 b and 12 b to the bearing member 13 via the flanges 11 d and 12 d at a time of molding with respect to the metal tube 1. Accordingly, the thrust load generated at a time of reducing the diameter of the metal tube 1 by each of the ring-shaped tools 11 and 12, is transmitted to the frame 31 from the molding rings 11 b and 12 b via the fitting portion 13 c of the bearing member 13, and the guide member 33.

The frame 31 attaching the ring-shaped tools 11 and 12 thereto is fixed to one end portion of a spindle 36 rotatably supported with respect to a bridge groove 35. A pulley 37 a is fixed to the other end portion side of the spindle 36, and a belt 37 d is wound between the pulley 37 a and a pulley 37 c fixed to a driving mechanism 37 b including a motor, a variable speed gear and a speed reduction gear. Accordingly, it is possible to rotate the frame 31 at a desired rotating speed, by driving the driving mechanism 37 b.

In this case, the present embodiment utilizes the hydraulic cylinder 32 at a time of moving the ring-shaped tools 11 and 12 along the straight line 31 b of the frame 31, however, it is not necessary to limit to the hydraulic cylinder, but it is possible to employ any structure as far as the structure can achieve a reciprocating linear motion as well as transmitting the molding load necessary for reducing the diameter of the metal tube 1 to each of the ring-shaped tools 11 and 12.

In the molding apparatus A structured as mentioned above, it is possible to incline the axial core 1 a of the metal tube 1 gripped to the chuck 25 with respect to the axial core 31 a of the frame 31 by synchronously actuating the supply car driving apparatus 23, the carriage driving apparatus 27 and the rotating table 28, thereby revolving the chuck 25, and it is possible to bring an intersecting point between the axial cores 1 a and 31 a into line with the straight line 31 b formed in the frame 31. Further, it is possible to move the metal tube 1 inclined with respect to the axial core 31 a of the frame 31 along the axial core 1 a, while executing the diameter reducing work with respect to the metal tube 1.

Further, it is possible to reduce the diameter while continuously changing the angle of incline of the axial core 1 a of the metal tube 1 with respect to the axial core 31 a of the frame 31, by continuously actuating the supply car driving apparatus 23, the carriage driving apparatus 27 and the rotating table 28.

Further, in the molding apparatus A mentioned above, the structure is made such that the rotating table 28 is provided in the chuck 25, and the angle of the chuck 25 is changed by the rotating table 28, however, the structure is not limited to this structure, but the structure may be made such that the rotating table is provided in the frame 31 and the axial core 31 a of the frame 31 is inclined with respect to the axial core 1 a of the metal tube 1. In this case, it is preferable to structure such as to be capable of integrally revolving the driving systems 37 a to 37 d of the frame 31 including eth frame 31 and the spindle 36 by setting the rotating table in an uprising portion of the bridge groove 35.

Embodiment 3

Next, a description will be given of an embodiment of a first molding method in accordance with the present invention. First, a description will be given of a molding procedure in the case that a main tube of the metal tube 1 and the axial core of the diameter reducing portion are in line with each other with reference to FIG. 5A. The molding method corresponds to a basic procedure at a time of reducing the diameter in the end portion of the metal tube 1, and makes it possible to easily understand the embodiment mentioned below.

The supply car 22 is moved in the direction of the arrow a or the direction of the arrow b by driving the supply car driving apparatus 23, and the axial core of the chuck 25 (the axial core 1 a of the metal tube 1) is brought into line with the axial core 31 a of the frame 31. At the same time, the axial core of the chuck 25 is brought into line with the axial core 31 a of the frame 31 by driving the rotating table 28.

The axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved so as to be approximately brought into line with the axial core 31 a of the frame 31, by driving the hydraulic cylinder 32 attached to the frame 31. The movement is executed for the purpose of passing the metal tube 1 through the rims 11 c and 12 c provided in the molding rings 11 b and 12 b of the respective ring-shaped tools 11 and 12. Accordingly, it makes no difference whether or not the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are accurately brought into line with the axial core 31 a of the frame 31, and in the case that the outer diameter of the metal tube 1 is sufficiently smaller than the inner diameter of the rims 11 c and 12 c provided in the molding rings 11 b and 12 b of the respective ring-shaped tools 11 and 12, it is not necessary to accurately bring them into line with each other.

Next, the end portion of the metal tube 1 is passed through each of the ring-shaped tools 11 and 12 by gripping the metal tube 1 to be reduced in diameter by the chuck 25, and driving the carriage driving apparatus 27. At this time, a length of the end portion of the metal tube 1 passed through each of the ring-shaped tools 11 and 12 is equal to a previously set length of the end portion to be reduced in diameter. Next, the rims 11 c and 12 c of the respective ring-shaped tools 11 and 12 are brought into contact with the outer periphery of the metal tube 1 by driving the hydraulic cylinder 32. A preparation for executing the diameter reduction is finished in this state.

The frame 31 is rotated at a previously set rotating speed by driving the driving mechanism 37 c. Two hydraulic cylinders 32 are simultaneously driven in accordance with the rotation start of the frame 31, and the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved in such a manner as to move away from the axial core 1 a of the metal tube 1. Since the rims 11 c and 12 c apply the molding load to the outer periphery of the metal tube 1 in accordance with this movement, the end portion of the metal tube 1 is reduced in diameter. It is possible to reduce the diameter in the end portion of the metal tube 1, by driving the carriage driving apparatus 27 in correspondence to the start of the diameter reduction, and moving the metal tube 1 in the direction of the arrow c or the direction of the arrow d.

In the process of the diameter reduction with respect to the end portion of the metal tube 1 mentioned above, the axial core 1 a of the metal tube 1 and the axial core 31 a of the frame 31 are held in a state of being brought into line with each other. Accordingly, the axial core of the reduced diameter portion is in line with the axial core 1 a of the metal tube 1. Further, it is possible to set the taper angle in the end portion of the metal tube 1 by controlling a moving speed of each of the ring-shaped tools 11 and 12 along the guide bar 33 by means of the hydraulic cylinder 32, and a moving speed in the direction of the arrows c and d of the metal tube 1 by means of the carriage driving apparatus 27.

Embodiment 4

Next, a description will be given of a case of reducing a diameter in a taper shape having an axial core which is in parallel to the axial core 1 a at an eccentric position (an amount of eccentricity a) from the axial core 1 a of the metal tube 1, with reference to FIG. 5B.

First, the axial core 1 a of the metal tube 1 is made eccentric at a previously set amount of eccentricity α from the center 31 a of the frame 31, by driving the supply car driving apparatus 23. Further, each of the ring-shaped tools 11 and 12 is moved by driving the hydraulic cylinder 32.

Further, the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved in such a manner as to be moved away from the center 31 a of the frame 31, by gripping the metal tube 1 by the chuck 25 so as to pass the end portion through each of the ring-shaped tools 11 and 12, thereafter rotating the frame 31 in the same manner as the embodiment 3 mentioned above, and simultaneously driving two hydraulic cylinders 32. The rims 11 c and 12 c can be brought into pressure contact with the outer periphery of the metal tube 1 so as to reduce the diameter in accordance with the movement. Further, it is possible to reduce the diameter in the end portion of the metal tube 1 in the taper shape around the axial core which is eccentric from the axial core 1 a, by driving the carriage driving apparatus 27 so as to move the metal tube 1 in the direction of the arrow c or the direction of the arrow d.

Embodiment 5

Next, a description will be given of an embodiment of a second molding method in accordance with the present invention. First, a description will be given of a case of reducing a diameter in the end portion of the metal tube 1 while moving the axial core 1 a of the metal tube 1 and the axial core 31 a of the frame 31 with time and relatively, with reference to FIG. 6A.

First, the axial core of the chuck 25 (the axial core 1 a of the metal tube 1) is brought into line with the axial core 31 a of the frame 31 by driving the supply car driving apparatus 23 and the rotating table 28. Further, each of the ring-shaped tools 11 and 12 is moved so as to be capable of accommodating the metal tube 1 by driving the hydraulic cylinder 32.

Next, the end portion is passed through each of the ring-shaped tools 11 and 12 by gripping the metal tube 1 by the chuck 25. In this state, the axial core 1 a of the metal tube 1 and the axial core 31 a of the frame 31 are in line with each other. Thereafter, the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved in such a manner as to be moved away from the axial core 31 a of the frame 31, by rotating the frame 31, and simultaneously driving two hydraulic cylinders 32. The rims 11 c and 12 c are brought into pressure contact with the outer periphery of the metal tube 1 in accordance with the movement, and the diameter reduction is started.

The metal tube 1 is moved in the direction of the arrow c or the direction of the arrow d by driving the carriage driving apparatus 27 in accordance with the start of the diameter reduction with respect to the end portion of the metal tube 1 caused by each of the ring-shaped tools 11 and 12, and the drive of the supply car driving apparatus 23 is simultaneously started. A moving length of the carriage 26 in the direction of the arrow c or the direction of the arrow d is set to be equal to the previously set length of the reduced diameter portion in the end portion of the metal tube 1. It is possible to pass the center 31 a (the straight line 31 b) of the frame 31 through a locus on a line β shown in FIG. 6A by moving the supply car 22 at the previously set distance α (the amount of eccentricity α) in the direction of the arrow b, during the period that the carriage 26 continues the movement mentioned above, whereby it is possible to mold in a state of inclining at an angle θa with respect to the axial core 1 a of the metal tube 1.

Further, when the moving amount of the supply car 22 in the direction of the arrow b becomes equal to the previously set amount of eccentricity α, it is possible to mold the reduced diameter portion having the axial core 1 b inclined at the angle θa with respect to the axial core 1 a of the metal tube 1, in the end portion of the metal tube 1. In the present embodiment, as shown in FIG. 6A, a boundary line between the metal tube 1 and the reduced diameter portion is formed within a surface which is approximately vertical to the axial core 1 a of the metal tube 1.

Embodiment 6

Next, a description will be given of a case of molding a reduced diameter portion inclined at an angle θb with respect to the axial core 1 a of the metal tube 1, with reference to FIG. 6B.

First, an angle of incline of the axial core 1 a of the metal tube 1 gripped to the chuck 25 with respect to the axial core 31 a of the frame 31 is set to θb by rotating the rotating table 28, for example, in a direction of an arrow e. Next, the carrier car 22 is moved, for example, in the direction of the arrow b, in such a manner that the axial core 1 a of the metal tube 1 gripped to the chuck 25 is in line with the center 31 a (the straight line 31 b) of the frame 31, by driving the supply car driving apparatus 23. Further, each of the ring-shaped tools 11 and 12 is moved so as to be capable of accommodating the metal tube 1 inclined at the angle θb by driving the hydraulic cylinder 32.

Next, the end portion is passed through each of the ring-shaped tools 11 and 12 by gripping the metal tube 1 by the chuck 25, thereafter, the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved in such a manner as to be moved away from the axial core 31 a of the frame 31, by rotating the frame 31, and simultaneously driving two hydraulic cylinders 32, in the same manner as the embodiment 3 mentioned above. The rims 11 c and 12 c are brought into pressure contact with the outer periphery of the metal tube 1 in accordance with the movement, and the diameter reduction is started.

It is possible to mold the reduced diameter portion having the axial core 1 b inclined at the angle θb with respect to the axial core 1 a in the end portion of the metal tube 1, by synchronizing the movement in the direction of the arrow d of the metal tube 1 caused by driving the carriage driving apparatus 27, and the movement in the direction of the arrow b of the supply car 22 caused by driving the supply car driving apparatus 23, in a state of maintaining the angle of incline of the rotating table 28, after the diameter reduction in the end portion of the metal tube 1 is started. In the present embodiment, as shown in FIG. 6B, a boundary line between the metal tube 1 and the reduced diameter portion is formed within a surface inclined at the angle θb with respect to the axial core 1 a of the metal tube 1.

Embodiment 7

A description will be given of a case of molding while continuously inclining the axial core 1 b of the reduced diameter portion from a state of bringing the axial core 1 b into line with the axial core 1 a of the metal tube 1 to an angle θc, with reference to FIG. 6C.

First, the axial core of the chuck 25 (the axial core 1 a of the metal tube 1) is brought into line with the axial core 31 a of the frame 31 by driving the supply car driving apparatus 23 and the rotating table 28. Further, each of the ring-shaped tools 11 and 12 is moved in such a manner as to accommodate the metal tube 1 by driving the hydraulic cylinder 32.

Next, the end portion is passed through each of the ring-shaped tools 11 and 12 by making the chuck 25 grip the metal tube 1. Thereafter, the axial cores 11 a and 12 a of the respective ring-shaped tools 11 and 12 are moved in such a manner as to be moved away from the axial core 31 a of the frame 31 by rotating the frame 31 and simultaneously driving two hydraulic cylinders 32. The rims 11 c and 12 c are brought into pressure contact with the outer periphery of the metal tube 1 in accordance with the movement, and the diameter reduction is started.

There are synchronously actuated the rotation of the rotating table 28, for example, in a direction of an arrow e, the movement of the metal tube 1 in a direction of an arrow d caused by driving the carriage driving apparatus 27, and the movement of the supply car 22 in a direction of an arrow b caused by driving the supply car driving apparatus 23, respectively in accordance with the start of the diameter reduction applied to the metal tube 1. In other words, it is possible to continuously increase the angle of incline of the axial core 1 b of the diameter reduced portion with respect to the axial core 1 a of the metal tube 1, by increasing the angle of incline of the axial core 1 b with respect to the axial core 1 a by continuously rotating the rotating table 28 in correspondence to the increase of the moving distance in the direction of the arrow d of the metal tube 1 generated by the carriage driving apparatus 27, and simultaneously increasing the moving distance in the direction of the arrow b of the supply car 22 by means of the supply car driving apparatus 23.

Further, in the case that the moving distance in the direction of the arrow d of the metal tube 1 by means of the carriage driving apparatus 27, the angle of rotation of the rotating table 28, and the moving distance in the direction of the arrow b of the supply car 22 by means of the supply car driving apparatus 23, respectively reach the previously set times and the previously set values, it is possible to mold the diameter reduced portion having the axial core 1 b which is inclined continuously to the angle θc from the original coinciding state with the axial core 1 a in the end portion of the metal tube 1. In the present embodiment, as shown in FIG. 6C, the boundary line between the metal tube 1 and the diameter reduced portion is formed within the surface which is approximately vertical to the axial core 1 a of the metal tube 1.

In each of the embodiments mentioned above, the description is given of the case that the end portion of the metal tube 1 is reduced in diameter in the tapered shape to the terminal end, however, it is not always necessary to mold in the tapered shape to the terminal end of the metal tube 1, but the terminal end portion of the metal tube 1 may be formed in a straight tube shape, as shown in FIG. 2.

INDUSTRIAL APPLICABILITY

In accordance with the molding method of the present invention mentioned above, it is possible to rationally reduce the diameter in the end portion of the metal tube to be reduced in diameter by applying the eccentric rotational molding method, and it is possible to preferably utilize the molding method of the present invention as a manufacturing means of a seamless diameter reduced portion in a piping distributing a fluid, in the manufacturing means of the exhaust gas converter.

Further, since the molding apparatus in accordance with the present invention can rationally execute the molding method in accordance with the present invention, can prevent the buckling which may be generated in the metal tube to be molded, and can preferably reduce the diameter by one step, the molding apparatus in accordance with the present invention can be preferably utilized in a factory reducing the diameter of the metal tube or the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions. 

1. A molding method of reducing a diameter in an end portion of a metal tube comprising the following steps: a step of arranging a plurality of ring-shaped tools arranged with an axial core which is in parallel to an axial core of the metal tube having the end portion to be reduced in the diameter and having an inner periphery brought into contact with an outer periphery of said metal tube, in a radial direction of a frame having an axial core which is in parallel to the axial core of the metal tube; a step of arranging said plurality of ring-shaped tools in such a manner that an axial core of each of the ring-shaped tools is in parallel to the axial core of the metal tube and an inner periphery is brought into contact with the outer periphery of said metal tube or is not brought into contact therewith, and a step of arranging so as to pinch the metal tube; and a step of rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged, and moving the axial core of the ring-shaped tool away from the axial core of the metal tube while moving the metal tube or the frame, thereby reducing the diameter in the end portion of the metal tube.
 2. A molding method of reducing a diameter in an end portion of a metal tube according to claim 1, wherein the method reduces the diameter in the end portion of said metal tube in a tapered shape having an axial core coinciding with the axial core of the metal tube, by previously bringing the axial core of said metal tube into line with the axial core of the frame.
 3. A molding method of reducing a diameter in an end portion of a metal tube according to claim 1, wherein the method reduces the diameter in the end portion of said metal tube in a tapered shape having an axial core which is eccentric from the axial core of the metal tube, by previously make the axial core of said metal tube eccentric from the axial core of the frame.
 4. A molding method of reducing a diameter in an end portion of a metal tube according to claim 1, wherein the method reduces the diameter in the end portion of the metal tube in a tapered shape having an axial core which is eccentric with respect to the axial core of the metal tube, by rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged, moving the metal tube or the frame in a direction in which the ring-shaped tools reach the end portion of the metal tube, and moving the axial core of the ring-shaped tools away from the axial core of the metal tube while moving the axial core of the metal tube away from the axial core of the frame in parallel.
 5. A molding method of reducing a diameter in an end portion of a metal tube while inclining at least a partial axial core of the end portion to be reduced in the diameter with respect to an axial core of the metal tube, at a time of reducing the diameter in the end portion of the metal tube, comprising the following steps: a step of arranging a plurality of ring-shaped tools rotating in a state in which an inner periphery is brought into contact with an outer periphery of the metal tube, in a radial direction of a frame and structuring an axial core of said frame and the axial core of the metal tube in such a manner as to be relatively changeable; a step of setting the axial core of said frame to a previously set angle with respect to the axial core of the metal tube and arranging said plurality of ring-shaped tools in such a manner that the inner periphery of each of the ring-shaped tools is brought into contact with the outer periphery of the metal tube or is not brought into contact therewith, a step of arranging so as to pinch the metal tube in said plurality of ring-shaped tools, thereafter rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged, and moving the metal tube or the frame, and moving the axial core of the ring-shaped tool away from the axial core of the metal tube while relatively changing the axial core of the frame and the axial core of the metal tube or without changing, in the process of moving said metal tube or the frame, thereby reducing the diameter in the end portion of the metal tube.
 6. A molding method of reducing a diameter in an end portion of a metal tube according to claim 5, wherein the method reduces the diameter in the end portion of said metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube, by previously bringing the axial core of said metal tube into line with the axial core of the frame, and relatively moving the axial core of the frame and the axial core of the metal tube in parallel in the process of moving the metal tube or the frame as well as rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.
 7. A molding method of reducing a diameter in an end portion of a metal tube according to claim 5, wherein the method reduces the diameter in the end portion of said metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube by previously inclining the axial core of the metal tube and the axial core of the frame relatively, and maintaining the incline between the axial core of the metal tube and the axial core of the frame in the process of moving the metal tube or the frame as well as rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.
 8. A molding method of reducing a diameter in an end portion of a metal tube according to claim 5, wherein the method reduces the diameter in the end portion of said metal tube in a tapered shape having an axial core inclined with respect to the axial core of the metal tube, by setting the axial core of the metal tube and the axial core of the frame to a previously set angle, and relatively changing the angle between the axial core of the metal tube and the axial core of the frame together with the movement of said metal tube or the frame, in the process of moving the metal tube or the frame as well as rotating said metal tube around the axial core or rotating the frame in which a plurality of ring-shaped tools are arranged.
 9. A molding apparatus for reducing a diameter in an end portion of a metal tube, comprising: a plurality of ring-shaped tools rotating in a state in which an inner periphery is brought into contact with an outer periphery of the metal tube; a frame arranging and holding said plurality of ring-shaped tools in a radial direction; a tool moving member provided in said frame and moving the individual ring-shaped tool within a surface which is orthogonal to an axial core of each of the ring-shaped tools; a drive member rotating said frame; a grip member arranged so as to face to said frame and gripping the metal tube to be reduced in diameter in the end portion; and a supply car mounting said grip member and structured such as to be movable in a direction of moving said grip member mounting said grip member close to or away from said frame, and an orthogonal direction to said direction.
 10. A molding apparatus for reducing a diameter in an end portion of a metal tube according to claim 9, wherein the molding apparatus further comprises a revolving member provided in said frame or the grip member arranged so as to face to said frame and relatively changing the angle formed by the axial cores.
 11. A molding apparatus for reducing a diameter in an end portion of a metal tube according to claim 9, wherein a plurality of ring-shaped tools held by said frame are arranged at a uniform angle around the axial core of said frame.
 12. A molding apparatus for reducing a diameter in an end portion of a metal tube according to claim 11, wherein a plurality of ring-shaped tools held by said frame are arranged at positions facing at 180 degree. 